In radio communication systems, information (for example voice, image information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data) is transmitted between sending and receiving station via a radio interface with the aid of electromagnetic waves. In this scenario the stations may be different types of subscriber-side radio stations, radio access points or base stations, depending on the actual embodiment of the radio communication system. The electromagnetic waves are radiated here using carrier frequencies which lie in the frequency band provided for the respective system.
Radio communication systems are often embodied as cellular systems e.g. conforming to the GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) standard having a network infrastructure consisting of base stations, devices for monitoring and controlling the base stations, and further network-side devices. Frequencies around 900, 1800 and 1900 MHz are used for the established cellular GSM (Global System for Mobile Communication) mobile radio system. Systems of this type essentially transmit voice, fax and short messages SMS (Short Message Service), as well as digital data.
Apart from these (supralocal) cellular, hierarchical radio networks organized over a wide area, there are also wireless local area networks (WLANs) with a radio coverage area that is generally much more limited geographically. With a diameter of up to several hundred meters, the cells covered by the WLANs are so small in comparison with typical mobile radio cells that they are referred to as microcells. Local area networks (LANs) are generally understood to mean communication networks extending from several tens of meters to up to 10 kilometers. However, the majority of LANs extend only over several hundred meters within buildings or within an organization (in-house networks).
Examples of different standards for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM, although at the present time, particularly in the USA and Europe, products based on the IEEE 802.11 family appear to be establishing themselves almost exclusively as local radio-based networks. The radio interface defined according to the IEEE 802.11b standard for accessing local area networks corresponds in terms of functionality to a wired connection to local area networks (LANs), which nowadays have evolved into the standard in offices.
The non-licensed frequency range around 2.4 GHz is generally used for WLANs. Data transfer rates are in the range of up to 11 Mbps. Future WLANs could be operated in the 5 GHz range and attain data rates of more than 50 Mbps. Thus, subscribers to the WLANs have available to them data rates that are substantially higher than those that are offered by the next, third mobile radio generation (e.g. UMTS). This means that access to WLANs for connections with high bit rates is to be preferred for the transfer of large volumes of data, particularly in connection with internet accesses.
WLAN can be used to build a wireless local area communication network wherein radio stations can communicate with one another by radio via one or more hops (hop, multihop) and/or via WLAN radio access points (AP: Access Point). A connection to broadband data networks (BDNs) can be implemented via the WLAN radio access points. WLANs are frequently used to supplement cable-based LANs in certain working environments, so the radio access points, which are possibly interconnected via a wire-based LAN, forward the data transport from a radio station via the LAN. Each radio access point typically provides coverage for all the radio stations located in its radio transmission range or, as the case may be, its radio coverage area.
If a radio access point is located outside of the radio transmission range of a radio station, it is possible for data to be transmitted between the radio station and the radio access point by using other radio stations to receive and forward the data. Toward that end it is necessary to determine a path between the radio station and the radio access point. In particular as a result of the mobility of radio stations, however, a path that has been determined does not remain in existence for an unlimited length of time. It is therefore possible that after sending data the sender receives an error message which notifies it that the path used hitherto has failed, with the result that the data currently cannot be transmitted via the path to the receiver. In this case the sender, i.e. either the radio station or the radio access point, once again initiates a method for determining a path to the receiver.